Repeaters for wireless communication systems

ABSTRACT

A flat-panel repeater includes a housing having a pair of oppositely facing surfaces, at least one antenna element mounted to each of the surfaces for radiating energy in a direction opposite to that of an antenna element mounted to the other of the surfaces, and an electronic circuit mounted within the housing and operatively coupling signals between at least one antenna element on each of the oppositely facing surfaces of the module. Isolation between the antennas on opposite sides of the repeater is improved by various techniques, such as use of adaptive cancellation which removes a significant portion of the feedback signal power, therefore increasing the total system isolation by the same amount. This additional isolation can be used to achieve greater system gain, and therefore significantly extend the range of the system. The repeater may also include a beamforming arrangement for creating a desired antenna pattern of one antenna relative to a base station and a desired antenna pattern of the other antenna relative to subscriber equipment.

FIELD OF THE INVENTION

The invention relates generally to repeaters for use in wirelesscommunication systems.

SUMMARY OF THE INVENTION

The present invention provides a flat-panel repeater system having ahousing having a pair of oppositely facing surfaces, at least oneantenna element mounted to each of the surfaces for radiating energy ina direction opposite to that of an antenna element mounted to the otherof the surfaces, and an electronic circuit mounted within the housingand operatively coupling signals between at least one antenna element oneach of the oppositely facing surfaces of the module.

One preferred embodiment of the invention improves isolation between theantennas on opposite sides of the flat-panel repeater by use of adaptivecancellation which removes a significant portion (between 10 dB and 40dB) of the feedback signal power, therefore increasing the total systemisolation by the same amount (10 to 40 dB). This additional isolationcan be used to achieve greater system gain, and therefore significantlyextend the range of the system. The cancellation scheme uses digitallyprocessed information to generate a signal, which, when added to theoriginal input signal, cancels the feedback signal. This is especiallyuseful in a side-side repeater.

In one particular embodiment of the invention having abase-station-facing antenna mounted on one of the opposing sides of thehousing and a mobile-facing antenna mounted on the other of the opposingsides of the housing, the two antennas each comprise an array of antennaelements, and a beamforming arrangement creates a desired antennapattern of the base-station-facing antenna relative to a base stationand a desired antenna pattern of the mobile-facing antenna relative tosubscriber equipment.

In a further aspect of the invention, the problem of equal gaincombining with a mobile signal source is overcome by the use ofpolarization diversity in a repeater. The vertical and horizontal fieldcomponents in a communications link are highly uncorrelated, and thus byusing receive antennas that have the same phase center and orthogonalpolarizations, the problem of location-induced phase variation iseliminated. Therefore, an equal gain combiner can be utilized that has afixed phase adjustment dependent only on the fixed phase differences ofthe repeater equipment, and not upon the changing location of the mobilesignal source.

The invention provides a repeater diversity system comprising a mainnull antenna having a given phase center and polarization for receivinga communications signal from a remote signal source, a donor antenna fortransmitting a signal to a base station, a diversity null antenna havingthe same phase center as the main null antenna and a polarizationorthogonal to the polarization of the main null antenna, a combiningnetwork coupled to the main null antenna and the diversity null antennafor combining the signals therefrom, and an uplink channel modulecoupled with the combining network for delivering diversity combinedreceive signals to the donor antenna.

Another aspect of the invention uses simple RF electronics, and Butlermatrix technology, to provide a mechanism to electronically steer anantenna beam toward the direction of the base station. A planar antenna,which may have a multiplicity of antenna elements, is used to generate aplurality of RF beams, via the RF Butler matrix. Each beam is presentedto an RF switch. The controlled switch toggles each beam, and the bestbeam is selected for RF input/output port(s). Additionally, the use ofthis antenna results in a narrow beam that reduces view to interferingsignals and therefore increases the carrier-to-interference (C/I) ratioof the system.

The invention provides a radio frequency switched beam planar antennasystem comprising a support structure, a plurality of antenna elementsmounted to the support structure, a Butler matrix mounted to the supportmember, the Butler matrix having a plurality of inputs coupledrespectively with the antenna elements and a plurality of outputs, and aradio frequency switching circuit mounted to the support structure andoperatively coupled with the outputs of the Butler matrix and having acontrol port responsive to a control signal for causing the switchingcircuit to select one of the outputs of the Butler matrix at a time.

The present invention also provides a system for re-transmitting a GPSsignal or other received satellite signals inside a structure. Thesystem receives the satellite signal, amplifies the received signal toproduce a second satellite signal, and re-transmits the second signalinside the structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a flat-panel repeater embodying theinvention;

FIG. 2 is an exploded perspective view of the repeater of FIG. 1;

FIG. 3 is a perspective view of another flat-panel repeater embodyingthe invention;

FIG. 4 is an exploded view of the repeater of FIG. 3;

FIG. 5 is a schematic representation of a repeater module in accordancewith one embodiment of the invention;

FIG. 6 is a schematic representation of another form of repeater modulein accordance with another embodiment of the invention;

FIG. 7 is an enlarged end elevation of one of the RF choke frames in therepeater of FIGS. 3 and 4;

FIG. 8 and FIG. 9 are a perspective view and a partial side sectionalview of another embodiment of an RF choke structure for a flat-panelrepeater;

FIG. 10 and FIG. 11 are a perspective view and a partial side sectionalview of another embodiment of an RF choke structure for a flat-panelrepeater;

FIG. 12 and FIG. 13 are a perspective view and a partial side sectionalview of another embodiment of an RF choke structure for a flat-panelrepeater;

FIG. 14 and FIG. 15 are side sectional and top views, respectively, of areduced surface wave (RSW) patch antenna;

FIG. 16 is a simplified perspective illustration of one form offlat-panel repeater in accordance with one form of the invention;

FIG. 17 is a simplified illustration of a second form of flat-panelrepeater in accordance with the invention;

FIG. 18 is a simplified perspective illustration showing anotherembodiment of a flat-panel repeater;

FIG. 19 is a diagrammatic representation of an in-building repeatersystem in accordance with the invention;

FIGS. 20 and 21 are simplified illustrations of repeater modules inaccordance with other forms of the invention;

FIG. 22 is a diagrammatic representation of another form of in-buildingrepeater system in accordance with the invention;

FIG. 23 a is a diagrammatic illustration of a system for distributingsignals from multiple wireless services throughout a building;

FIG. 23 b is a diagrammatic illustration of a PCS converter used in thesystem of FIG. 23 a;

FIG. 24 is a block diagram of one signal path through a repeater system;

FIG. 25 is a block diagram of one signal path through a repeater system,as in FIG. 24, adding an adaptive cancellation circuit;

FIG. 26 is a block diagram (high level) of a (digitally) adaptivecancellation circuit in accordance with one embodiment of the invention;

FIG. 27 is a block diagram (high level) of the (digitally) adaptivecancellation circuit of FIG. 26 which shows the technique in furtherdetail;

FIG. 28 is a block diagram of a repeater system, similar to that of FIG.17, using the adaptive cancellation (AC) circuit of FIGS. 26 and 27;

FIGS. 29 and 30 show the directional characteristics of the AC blocks,for the downlink path (FIG. 29) and the uplink path (FIG. 30);

FIGS. 31 and 33 show two examples of side-to-side repeaters;

FIGS. 32 and 34 show block diagrams of the side-to-side repeater systemsof FIGS. 31 and 33, respectively, with the addition of adaptivecancellation;

FIG. 35 is a simplified view of a repeater system of the prior art;

FIG. 36 is a simplified view, in a form similar to FIG. 35, showing arepeater in accordance with one embodiment of the invention;

FIG. 37 is a diagrammatic illustration of beam steering in an integratedrepeater system of the invention;

FIG. 38 is a block schematic diagram of one form of a repeater inaccordance with the invention, utilizing a duplexed antenna;

FIG. 39 is a block schematic similar to FIG. 38 but illustratingimplementation with separate transmit and receive antennas;

FIG. 40 is a simplified illustration of a patch antenna array;

FIG. 41 is a simplified representation, in a form similar to FIG. 40, ofa dipole antenna array;

FIGS. 42 and 43 are flowcharts or flow diagrams of a repeater setupprogram in accordance with one embodiment of the invention;

FIG. 44 is a flowchart or flow diagram of one embodiment of a repeatermain operation loop;

FIG. 45 is a functional diagram showing beamsteering via a Butlermatrix;

FIG. 46 is a simplified schematic diagram showing beamsteering usingphase shifters;

FIG. 47 is a perspective view of a flat-panel repeater design;

FIG. 48 is a perspective view illustrating a beamsteering scheme viatilting of flat panel arrays similar to the flat panel array of FIG. 47;

FIG. 49 and FIG. 50 are two diagrammatic representations of beamsteeringusing striplines of different lengths,

FIG. 51 is a perspective view of a solar-powered battery for a repeater;

FIG. 52 is a diagrammatic illustration of a modified in-buildingrepeater system using physically separated antennas;

FIGS. 53-53 g are diagrammatic illustrations of modified repeaters usingphysically separated antennas;

FIG. 54 is a diagrammatic illustration of another modified repeaterusing physically separated antennas;

FIG. 55 is a functional block diagram of a single repeater cell of aside-to-side repeater for a TDD communication system in accordance withone form of the invention;

FIG. 56 shows in diagrammatic form multiple cells having the generalconfiguration shown in FIG. 55;

FIG. 57 is a somewhat diagrammatic view showing a repeater in accordancewith one form of the invention;

FIG. 58 is a simplified elevation showing a repeater tower structure inaccordance with one embodiment of the invention;

FIG. 59 is a circuit schematic illustrating a diversity repeater systemin accordance with one embodiment of the invention;

FIG. 60 is a circuit schematic illustrating a diversity repeater systemin accordance with a second embodiment of the invention;

FIG. 61 is a simplified showing of two antennas having the same phasecenter and mutually orthogonal polarizations;

FIG. 62 is a block diagram showing a plurality of antenna elementscoupled to an RF Butler matrix;

FIG. 63 shows an example of a beam pattern for one of the spatial(antenna) elements of FIG. 62;

FIG. 64 shows a system, similar to FIG. 62 using four antennas;

FIG. 65 shows an approximate azimuth beamwidth response for the Butlermatrix in FIG. 64;

FIG. 66 is a plan view, somewhat diagrammatic in form, of a planarswitched beam antenna system;

FIG. 67 is a simplified top view of one of the patch antenna elements ofthe system of FIG. 66;

FIG. 68 is a simplified diagram of an RF switch of the system of FIG.66;

FIG. 69 is a block diagram of the circuit of FIG. 66;

FIG. 70 is a block diagram similar to FIG. 69 with an RF to IFtransceiver (transverter) added;

FIG. 71 is a block diagram similar to FIG. 70 with a modem added;

FIG. 72 is a simplified perspective view of a planar system (unit),indicating the elements of FIG. 71;

FIG. 73 is a view, similar in form to FIG. 66, showing an embodimenthaving separate transmit and receive antenna elements;

FIG. 74 is a block diagram of the circuit of FIG. 73;

FIG. 75 shows the circuit of FIG. 74, adding an RF to IF downconverter(or receiver) for the receive mode, and IF to RF upconverter (ortransmitter/exciter) for the transmit mode;

FIG. 76 shows the circuit of FIG. 75, adding a modem;

FIG. 77 shows a system similar to FIG. 66, using elevation arrays inplace of single array elements;

FIG. 78 is a simplified view in a form similar to FIG. 720, showing 360degree coverage, employing two such systems, back to back, to generate,in effect, an omni-directional system;

FIG. 79 shows an alternative structure for obtaining 360 degreecoverage, using dipole antenna elements on a PCB;

FIG. 80 shows approximate azimuth beams for the system of FIG. 79;

FIG. 81 is a simplified perspective view showing an indoor installationof a system in accordance with the invention;

FIG. 82 is a perspective view of a flat panel antenna for a laptop orsimilar portable computer; and

FIG. 83 is a perspective view showing a laptop computer with the flatpanel antenna of FIG. 82.

FIG. 84 is a diagrammatic top plan view of a repeater having multiplemobile-facing antennas to provide wider angle coverage;

FIG. 85 is a schematic diagram of an electronic system for use in therepeater of FIG. 84;

FIG. 86 is a diagrammatic top plan view of a repeater having a modifiedmobile-facing antenna for providing wide-angle coverage;

FIG. 87 is a diagrammatic top plan view of a repeater having anothermodified mobile-facing antenna for providing wide-angle coverage;

FIG. 88 is a diagrammatic top plan view of a repeater having amobile-facing base-station-facing antennas in planes that are notparallel to each other;

FIG. 89 is a diagrammatic side elevation of a building containing arepeater for re-transmitting signals in a direction orthogonal to thedirection in which the signals are received;

FIG. 90 is a structure that includes a GPS repeater system according toone embodiment of the invention;

FIG. 91 is another structure that includes a GPS repeater systemaccording to another embodiment of the invention;

FIG. 92 is a block diagram of a primary GPS repeater used in the GPSrepeater systems of FIGS. 90 and 91;

FIG. 93 is a block diagram of one embodiment of a gain block used in theprimary GPS repeater of FIG. 92;

FIG. 94 is a block diagram of another embodiment of the gain block ofFIG. 92;

FIG. 95 is a block diagram of another primary GPS repeater used in theGPS repeater systems of FIGS. 90 and 91;

FIG. 96 is a block diagram of one embodiment of a gain block used in theprimary GPS repeater of FIG. 95;

FIG. 97 is a block diagram of a secondary GPS repeater used in the GPSrepeater system of FIG. 91; and

FIG. 98 is a block diagram of one embodiment of a gain block used in thesecondary GPS repeater of FIG. 97.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1 and 2 illustrate a preferred embodiment of a flat-panelrepeater, having a pair of flanged radomes 10 and 11 on opposite sidesof a choke frame 12. Adjacent the inside surface of the radome 10 is adielectric sheet 13 carrying four printed dipoles 14 that form themobile-facing antenna for the mobile side of the repeater. Theelectronics for connecting the antenna to the necessary diplexers,filters, and power amplifiers are contained within a metal housing 15,and the antenna sheet 13 is fastened to one side of the housing 15. Theantenna feed 16 is connected directly to one of the diplexers in theelectronic circuitry, which will be described in more detail below. Thehousing 15 is captured within the choke frame 12, which forms multiple,spaced, concentric fins 72 a-72 d for improving the side-to-side(antenna-to-antenna) isolation of the flat-panel repeater, therebyimproving the gain performance or stability margin (the difference orsafety margin between isolation and gain). The structure of the fins 72a-d will also be described in more detail below.

The antenna elements on the opposite side of the repeater are mountedadjacent the inside surface of the radome 11. Thus, a pair of dipoles 14a are printed on a dielectric sheet 13 a to form the base-station-facingantenna for the base-station side of the repeater. The antenna feed 16 ais connected directly to one of the diplexers in the electroniccircuitry, as described in more detail below. The dielectric sheet 13 ais fastened to the opposite side of the metal housing 15 from the sheet13. As can be seen in FIG. 2, the dipoles 14 are orthogonal to thedipoles 14 a to improve isolation between the two antennas.

To facilitate mounting of the repeater on a flat surface, a mountingbracket 17 has a stem 18 that fits into a socket 19 in the frame 12. Thebracket 17 has several holes through it to receive screws for attachingthe bracket 17 to the desired surface. Electrical power can also besupplied to the repeater through power supply lines (not shown) passingthrough the mounting bracket 17 and its stem 18 into the frame 12. Theinterface between the frame 12 and the bracket stem preferably allowsrotation between the frame 12 and the mounting bracket 17 in successiveangular increments, such as 5° increments, to facilitate precisepositioning of the repeater. For example, the repeater might be rotatedthrough successive increments while monitoring the strength of thereceived and/or transmitted signals, to determine the optimumorientation of the repeater, e.g., in alignment with a broadcast antennawhose signals are to be amplified and re-broadcast. Conventional detentscan be used to indicate the successive increments, and to hold therepeater at each incremental position until it is advanced to the nextposition.

As can be seen in FIG. 1, the flat-panel repeater comprises a closelyspaced stacked array of planar components that form a compact unit thatcan be easily mounted with the antennas already aligned relative to eachother. The height and width of the unit are a multiple of the thicknessdimension, e.g., 7 to 8 times the thickness. The thickness dimension ispreferably no greater than about six inches, and the greater of saidheight and width dimensions is preferably no greater than about twofeet. It is particularly preferred that the thickness dimension be nogreater than about three inches, and the greater of said height andwidth dimensions no greater than about 1.5 feet. Most preferably, thethickness dimension is no greater than about two inches, and the greaterof the height and width dimensions is no greater than about one foot.

FIGS. 3 and 4 illustrate a flat-panel repeater 20 having a pair of flatradomes 21 and 22 on opposite sides thereof. Each radome 21 and 22covers one or more antenna elements for receiving and transmittingsignals on opposite sides of the repeater. In the illustrativeembodiment, the antenna elements are the patches of patch-type antennas,but it will be understood that alternative antenna elements such asdipoles or monopoles may be used. As can be seen in FIG. 4, a pair ofpatches 23 and 24 are printed on a dielectric plate 25 mounted adjacentthe inside surface of the radome 21. The dielectric plate 25 seats in arecess 27 formed by a metal plate 28 that also forms a ground plane forthe patches 23 and 24. The plate 25 seats on multiple plastic standoffs27 a connected to the plate 28 within the recess 27, and a pair ofcoaxial connectors 27 b extend through he plate 28 for connection to thepatches 23 and 24. The inner conductors of the connectors 27 b areconnected to the patches 23 and 24, while the outer conductors areconnected to the ground plane 28. The opposite ends of the connectors 27b are connected to the RF circuitry on the board 36. Because thedielectric plate 25 is recessed within the ground plane, the patches 23and 24 are substantially flush with the surface of the ground plane.

It can be seen that the ground plane formed by the metal plate 25 isconsiderably larger than the antenna patches 23 and 24, and the patchesare positioned in the central region of the ground plane. These featuresoffer significant advantages in improving the isolation between the twoantennas, which in turn improves the gain performance or stabilitymargin of the repeater, as will be discussed in more detail below. Ingeneral, the ratio of the total ground-plane area to the central areaoccupied by the antenna elements is in the range of about 2 to 5, and ispreferably about 5, to achieve the desired isolation.

The repeater 20 includes a three-part frame, consisting of a centralframe member 29 and a pair of RF-choke frames 30 and 31 attached toopposite sides of the central member 29. The periphery of theground-plane plate 27 is captured within a slot in the inner peripheryof the choke frame 30. The central frame member 29 is essentially closedon one side by an integral wall 32 that forms a bottom ground plane, andthe interior of the member contains several electronic units (e.g.,printed circuit boards) and a power connector 33. A top ground-planeplate 34 closes the open side of the frame member 29, and is attached toa peripheral flange 35 on the frame member 29. A second group ofelectronic units are mounted on a board 36 attached to the outside ofthe ground-plane plate 34.

The antenna elements on the opposite side of the repeater are mountedadjacent the inside surface of the radome 22. Thus, a pair of patches 37and 38 are printed on a dielectric plate 39 seated in a recess 40 formedby a metal plate 41 that also forms a ground plane for the patches 37and 38. As can be seen in FIG. 4, the patches 23, 24 are orthogonal tothe patches 37, 38 to improve isolation between the antennas on oppositesides of the repeater. The periphery of the ground-plane plate 41 iscaptured within a slot in the inner periphery of the second choke frame31. The patch plate 39 seats on multiple plastic standoffs 40 aconnected to the plate 41 within the recess 40, and a pair of coaxialconnectors 40 b extend through the plate 41 for connection to thepatches 37 and 38. The inner conductors of the connectors 40 b areconnected to the patches 37 and 38, while the outer conductors areconnected to the ground plane 41. The opposite ends of the connectors 40b are connected to the RF circuitry on the board 36. Multiple gaskets Gare provided for sealing purposes.

An antenna is (simplifying somewhat) a path by which electrons getaccelerated back and forth (i.e. a “race-track”). For example, in adipole antenna, electrons accelerate from one end, towards the center(where they have the greatest velocity), then de-accelerate towards theother end (where the velocity is the slowest). They then turn around andaccelerate back the other way. They do this at the rate of the resonantfrequency of the antenna. The feed point of the antenna (for a dipole,at the center) is the position in which the electrons are moving thefastest. Thus, voltage (potential) of the antenna is tapped from thisposition. Electromagnetic energy therefore radiates from the ends of anantenna element (dipole or patch) in the direction of the acceleratingelectrons. This direction is called the antenna polarization(direction). Displacement currents (virtual electrons) therefore go fromone end of the dipole, curve out in space, and terminate at the otherend of the dipole. For two adjacent antennas, oriented in the samedirection, where one is transmitting (active) and the other is receiving(passive), the active antenna pushes virtual electrons into space whichterminate on the passive antenna. These virtual electrons then force theactual electrons on the surface of the passive antenna to accelerate,and induce a potential at its feed point. However, if the two antennasare not oriented in the same direction (being orthogonal . . . orperpendicular; for instance) then the active antenna cannot accelerateelectrons on the other (passive) antenna. The “race-track” on thepassive antenna is extremely short. These antennas are consideredorthogonal, and therefore do not couple. Orthogonal antennas, onopposite sides of the repeater, do not couple and therefore appearisolated from each other. Thus, the system gain is increased withoutinducing ringing.

The RF electronic circuitry and antennas for the repeaters of FIGS. 1-4is illustrated in more detail in FIGS. 5-8. Two different systemarchitectures are shown in FIGS. 5 and 6. FIG. 5 shows an architecturefor a two-antenna system, in which each of two antennas 52 and 54operates in both the transmit and receive modes. For example, the firstantenna 52 might be used to receive incoming RF signals from, andtransmit signals to, a transmitter or another repeater, that is, in thelink mode. The other antenna 54 would then be utilized in thebroadcast/repeat mode to transmit signals to, and receive signals from,the user equipment, such as a remote handset or terminal, or to transmita signal to a further repeater in a system using multiple repeaters tobroadcast or distribute signals.

An electronics module 60 connected to both antennas 52 and 54 includes apair of frequency diplexers (D) 61, 62 to effectively connect receivedsignals from either antenna to only the receive circuitry for thatantenna and not to the transmit circuitry for that same antenna, and toeffectively connect transmit signals from the transmit circuitry to onlythe antenna and not to the receive circuitry for that same antenna. Forexample, RF signals received by the antenna 52 are routed through thediplexer 61 to a receive path that includes a filter 63 to attenuate thereverse link band, an amplifier 64 to amplify the RF, and then anotherfilter 65 to protect the amplifier 64 from signal power on the otherpath. The second diplexer 62 then delivers the signal to the antenna 54which re-transmits the amplified signal. In the reverse direction, theantenna 54 receives signals that are fed through the diplexer 62 to asecond path including similar filters 66, 67 and a similar amplifier 68which operate in the same manner as the first circuit to feed signalsthrough the diplexer 61 to be transmitted at the antenna 52.

FIG. 6 shows a four-antenna architecture that includes two pairs ofantennas 52 a, 54 a and 52 b, 54 b on opposite sides of the repeater.The antennas 52 a, 52 b on one side may be used for the link mode, asdescribed above, one as the downlink antenna and one as an uplinkantenna. Similarly, the two antennas 52 b, 54 b on the other side may beused in the broadcast/repeat mode, as described above, one as an uplinkantenna and one as a downlink antenna. Similar electronic circuits orpaths including filters and amplifiers are interposed between therespective pairs of antennas 52 a, 54 a and 52 b, 54 b. However, becauseseparate pairs of antennas are provided, no frequency diplexers arerequired in this case.

The filters 63, 65, 66, and 67 are band pass filters selected to reducethe out-of-band signals. For a PCS-based system, the typical band passbandwidth is approximately 15 MHz, commensurate with the bandwidth ofPCS bands C, D, E, F, etc. Cut off and roll-off are performance andspecification oriented, and depend on the circuit design.

In one embodiment, the amplifiers 64, 68 comprise relatively low power,linear integrated circuit chip components, such as monolithic microwaveintegrated circuit (MMIC) chips. These chips may comprise chips made bythe gallium arsenide (GaAs) heterojunction transistor manufacturingprocess. However, silicon process chips or CMOS process chips might alsobe utilized.

Some examples of MMIC power amplifier chips are as follows:

-   -   1. RF Microdevices PCS linear power amplifier RF 2125P, RF 2125,        RF 2126 or RF 2146, RF Micro Devices, Inc., 7625 Thorndike Road,        Greensboro, N.C. 27409, or 7341-D W. Friendly Ave., Greensboro,        N.C. 27410;    -   2. Pacific Monolithics PM 2112 single supply RF IC power        amplifier, Pacific Monolithics, Inc., 1308 Moffett Park Drive,        Sunnyvale, Calif.;    -   3. Siemens CGY191, CGY180 or CGY181, GaAs MMIC dual mode power        amplifier, Siemens AG, 1301 Avenue of the Americas, New York,        N.Y.;    -   4. Stanford Microdevices SMM-208, SMM-210 or SXT-124, Stanford        Microdevices, 522 Almanor Avenue, Sunnyvale, Calif.;    -   5. Motorola MRFIC1817 or MRFIC1818, Motorola Inc., 505 Barton        Springs Road, Austin, Tex.;    -   6. Hewlett Packard HPMX-3003, Hewlett Packard Inc., 933 East        Campbell Road, Richardson, Tex.;    -   7. Anadigics AWT1922, Anadigics, 35 Technology Drive, Warren,        N.J. 07059;    -   8. SEI Ltd. P0501913H, 1, Taya-cho, Sakae-ku, Yokohama, Japan;        and    -   9. Celeritek CFK2062-P3, CCS1930 or CFK2162-P3, Celeritek, 3236        Scott Blvd., Santa Clara, Calif. 95054.

FIGS. 7 and 8 show the choke frame of FIGS. 1 and 2 in more detail. Thisframe is generally rectangular in configuration and includes multiplefins 70 extending orthogonally outwardly from opposite sides of centralflat support members 71 and 72. As can be seen most clearly in thesectional view in FIG. 8, the fins 70 become progressively shorter inthe axial direction, and the space between adjacent fins becomesprogressively smaller, proceeding from the radially outermost fins 70 ato the innermost fins 70 d. The fins preferably have height and spacingdimensions related to one-fourth wavelength at the center frequency ofthe frequency band being amplified and re-transmitted by the repeater,e.g., the height or projection of the fins relative to the sides of thehousing may be on the order of a quarter wavelength. In addition, stripsof radio frequency absorber material 74 may be located intermediate someor all of the fins 70 about the peripheral surfaces of the main body ofthe choke frame. Absorber material is typically a low density dielectricloaded with conductive particles or fibers of carbon or metal, and caneven be “tuned” to absorb certain frequencies more than others.

FIG. 9 illustrates in more detail the peripherally extending fins 73that form the RF choke between the antennas on opposite sides of theflat-panel repeater of FIGS. 3 and 4. These fins 73 comprise relativelythin strips of conductive material located around the periphery of theRF choke frame. FIGS. 10-13 illustrate alternate embodiments of RFchokes of various forms.

In FIGS. 10 and 11, the RF choke is formed by a series of concentricannular rings 75 which extend generally orthogonally relative to theplane of the antenna and around the periphery of the antenna, incontrast to the radially extending fins described above. As can be seenmostly clearly in the sectional view of FIG. 11, the choke rings 75 areformed by a corrugated metal annulus in which the outer wall 75 a isslightly shorter than the first full corrugation crest 75 b in the axialdirection, and then the successive corrugation crests 75 c and 75 dbecome progressively shorter in both the axial and radial directions.

The circular choke configuration of FIGS. 10 and 11 has the advantage ofproviding feedback paths of equal length between all points on theperipheries of the antennas on opposite sides of the repeater. Unwantedfeedback occurs via surface currents on the outside surfaces of thepanel, and path lengths that are odd multiples of one-half wavelengthproduce cancellation of the unwanted surface currents. The circularconfiguration facilitates a choice of dimensions that achieve thedesired cancellation of feedback currents because of the uniformity ofthe lengths of the feedback paths between the two antennas with such aconfiguration. In general, the repeater is sized and configured for aselected frequency band having a predetermined center frequency andwavelength “X”; the height, width and thickness dimensions of therepeater are selected so that feedback energy at the wavelength “X”travels a feedback path of predetermined length around the repeater toimprove the side-to-side isolation.

FIGS. 12 and 13 illustrate a circular configuration for a chokestructure similar to that shown in FIGS. 8 and 9. Multiple fins 80extend orthogonally outwardly in the axial direction from opposite sidesof central flat support members 81 and 82. As can be seen most clearlyin the sectional view in FIG. 13, the fins 80 become progressivelyshorter in the axial direction, and the space between adjacent finsbecomes progressively smaller, proceeding from the radially outermostfins 80 a to the innermost fins 80 d.

In an alternative embodiment, a reduced surface wave (RSW) type ofantenna structure might be utilized in place of the patch antennas shownin the prior figures. FIGS. 14 and 15 are a side sectional view and atop plan view of one example of a probe-fed, shorted annular ring,reduced surface wave patch antenna 460. An RSW patch antenna element, issimply a patch that focuses more energy in the directed area, and not tothe sides near the ground plane. There are many types of RSW patches,but the most common is a recessed patch inside a partial cavity. Thecavity walls act as a field suppressor, and “catch” field lines that aredirected to the sides of the patch, rather than in a directionperpendicular to the patch and ground plane. If both patches (onopposite sides of the repeater) are RSW patches, then they have reducedcoupling (i.e. greater isolation), which allows the system active gainto be increased.

RSW microstrip antennas produce only a small amount of surface-waveradiation. In addition, if printed on electrically thin substrates,these antennas only weakly excite lateral waves (space waves thatpropagate horizontally along the substrate interface). As a result,these antennas do not suffer from the deleterious effects of surface andlateral wave scattering. These characteristics make the RSW antennaideal for applications where the supporting substrate or ground plane ofthe antenna is small, in which case diffraction of the surface andlateral waves from the edges of the structure may be quite significantfor conventional microstrip patch antennas. RSW antennas may also beuseful for array applications, where the presence of surface and lateralwaves for conventional patch radiators produce significant mutualcoupling and may lead to scan blindness.

For a given size antenna element (patch, dipole, etc.), increasing thesize of the ground plane behind the element reduces the Front to Back(F/B) ratio of the antenna. More specifically, the larger the groundplane, the less energy radiated to the back side. Thus, increasing thesize of the faces of the side-to-side repeater reduces the amount ofenergy that each face radiates to the backward face. Another way ofexplaining this is that by increasing the size of the repeater, thelower the coupling between the antennas on opposite sides of therepeater (i.e. patches). This therefore increases the isolation betweenthe antennas, and allows the active gain for the system to be increased.However, where the size of the ground plane is limited by otherconsiderations, the RSW patch technology may be employed.

A preferred RSW design is the Shorted-Annular-Ring Reduced-Surface-Wave(SAR-RSW) antenna. One example of this type of antenna, shown in FIGS.14 and 15, is a conventional annular ring microstrip antenna 462 with aninner boundary 464 short-circuited to a conducting ground plane 466. Theouter radius dimension is chosen to eliminate surface-wave excitationfrom the equivalent ring of magnetic current at the outer edge of theantenna that corresponds to the TM₀₁₁ cavity patch mode. (The modes aredenoted using the notation TM_(φρ).) The inner radius is chosen to makethe patch resonant at the design frequency.

FIGS. 16 and 17 diagrammatically illustrate repeater modules 50 and 50 awith patch antennas that correspond respectively to the systemsdescribed above. In these examples, microstrip patches are used for theantenna elements 52, 54 (FIG. 16) and 52 a, 52 b, 54 a, 54 b (FIG. 17).The module/box or housing 50, 50 a may contain a DC power supply or DCpower converter, amplifiers, filters and diplexers (if required), asdescribed above. The electronics may be discrete parts, connectedtogether via SMA connectors. For lower power systems, the electronicscan be surface mount PCB. A small lamp, LED, or other display element100 can be used with appropriate RF power sensing electronics 80 (seeFIGS. 5 and 6) to aid the provider/user/customer in orienting the unitor module 50 or 50 a with a link antenna directed/pointed towards a basestation, such that sufficient signal power is being received, i.e., ator above some predetermined threshold.

FIG. 18 illustrates an approach which uses an array of antenna elementsin order to increase the passive gain. The example shown in FIG. 18 usestwo columns of patch array antenna elements on one face of the module,designated by reference numerals 54 a through 54 h. The antenna patches54 a through 54 d are designated as receive (Rx) elements in theembodiment shown in FIG. 18, while the antenna elements 54 e through 54h are designated as transmit (Tx) elements in this embodiment. It willbe appreciated that a similar array of antenna elements, correspondingto the antenna elements 52 of the prior embodiments, are mounted to theopposite face (not shown) of the module 50 b of FIG. 18. Moreover, feweror more array elements might be utilized in other patterns than thatshown on FIG. 18, without departing from the invention.

In the embodiment shown on FIG. 18, the use of four elements, which aresummed together in an array, achieves approximately four times (6 dB)the gain of a single receive or transmit element. Thus, with fourelements also on the opposite face (not shown), this adds a total of 12dBi of additional passive gain to the system, which can be used toreduce the required active gain by as much as 12 dB and also to reducethe required isolation by as much as 12 dB. While the near-field wavemechanics might not permit a full 12 dB to be achieved, nonetheless,some considerable improvement can be expected from this approach. Thevertical beam width of the system will be reduced somewhat by thisapproach.

The antennas on opposite sides of the repeaters described above are“fixed” in position and orientation to assure maximum isolation betweenthe antennas and to receive and transmit a given signal, and thereforemaximize system gain. This isolation between antennas iscontrolled/maximized (and mutual coupling minimized) in the followingways:

-   -   a) The two antennas (or sets of antennas) are positioned such        that for each, the F/B ratios sum to a maximum. For example, for        a perfectly rectilinear module, the two antennas (or sets of        antennas) each face oppositely by 180 degrees, or within an        acceptable tolerance.    -   b) The two antennas of each path, are polarized in mutually        orthogonal (perpendicular) directions, which further reduces the        mutual coupling (increases the isolation) by roughly 20 to 30        dB.    -   c) Electromagnetic choke or shunt elements are provided on the        edges or borders of the module or housing structure to absorb        (shunt) power to ground. Alternatively, the four sides of the        housing (i.e., excluding the two sides on which the antennas are        mounted) may be composed of metallic material and grounded so as        to shunt stray electromagnetic energy to ground.

Design of the antennas, beams, and (control of) F/B ratios assuresadequate isolation between the two opposing antennas (or antenna sets).The antennas'F/B ratios or isolation is the largest limiter for thetotal system gain. If desired, the isolation can be further improved byhaving the wireless connection to the base station on a differentfrequency band from the remote connection.

The above described repeater modules can be used in a number ofapplications, a few examples of which are as follows.

1) Indoor Repeater (see FIG. 19)

The flat-panel repeater can be mounted on a wall or window, at or near alocation where the RF signal power from a nearby base station is at itsmaximum power level (within the building). Power for each repeater canbe supplied via either a 120-volt cord and plug 102, or with a 120-voltplug connection 104, built directly into the repeater (see FIGS. 20 and21). Both allow very simple installation, by the customer. Generally,the RF signal is received, at a power level above the noise floor, froma nearby base station (with the module placed in a location facing thebase station), and the repeater re-radiates the (amplified) RF signalinto the building. Additionally, signals from remote units(handsets/cellphones) within the building are received by the repeater,amplified, and re-radiated back to the base station 200.

2) Daisy-Chained Indoor Repeater (see FIG. 22)

FIG. 22 shows a plurality of flat-panel repeaters 50 or 50 a placed atvarious locations within a building, “daisy chained” together, toprovide greater coverage within the building. This aids in providingcoverage to the side of the building opposite to the base station, orany other RF null or “blank” areas within the building. In this way, theprovider or customer can cheaply and easily install two or morerepeaters, to provide coverage to various areas of the building, such asthe side opposite the side nearest the base station, where the RF signallevel (from the base station) has low Signal to Noise (ratio), or wherethere is no signal at all.

If it is desired to distribute multiple wireless services within abuilding, such as PCS, MMMDS, LMDS, wireless LAN, cellular telephone,etc., all such signals may be supplied from their receiving antenna(s)to an Ethernet hub before entering the daisy-chained indoor repeaters,as illustrated in FIGS. 23 a and 23 b. A separate antenna 110 andelectronic circuits 111 are provided for each wireless service, and allthe circuits 111 are connected to an Ethernet hub 112. Each of thecircuits 111 includes a frequency converter for converting signals fromthe frequency used by the wireless service to an Ethernet frequency. TheEthernet hub 112 controls the forwarding of the signals from themultiple wireless links to the single wired connection from the Ethernethub 112 to an indoor flat-panel repeater 113, which then relays thosesignals on to other repeaters such as repeaters 114 and 115 locatedthroughout the interior of the building.

Each of the repeaters 114 and 115 has two antennas on the downlink side.Specifically, a first antenna 114 a on the repeater 114 is designed toproduce a beam 117 aligned with the next repeater 115, while a secondantenna 114 b produces a beam 118 that extends laterally through theadjacent portion of the interior of the building to reach all the usersin that portion of the building. For user devices that are not part ofan Ethernet, such as PCS subscriber units, the signals from the secondantenna 114 b are received by an Ethernet-to-PCS conversion unit 119shown in more detail in FIG. 23 b. This conversion unit includes anantenna 119 a that complies with the IEEE 802.11 standard, a DSP 119 b,an RF conversion circuit 119 c for converting the frequency of receivedsignals to the PCS frequency, and a PCS antenna 119 d for transmittingthe converted signals to PCS users in the building. Of course, theconversion unit 119 also works in the reverse direction, receiving PCSsignals from subscriber units at the antenna 119 d, converting them tothe Ethernet frequency in circuit 119 c, and transmitting them fromantenna 119 a to the repeater 114 for re-transmission back to therepeater 113 and the Ethernet hub 112 which selects the appropriatecircuit 11 and antenna 110.

3) Outdoor Null Fill Repeater

A single flat-panel repeater can be installed on a tower, instead of amore conventional repeater installation requiring discrete antennas.This provides a smaller, more economical package, and less labor (time)and effort in orienting the antennas to assure adequate isolationbetween the antennas.

4) Outdoor Repeater to Building

A single flat-panel repeater can be installed on a tower, in the samefashion as above, realizing the same benefits.

The applications mentioned above in 1)-4) are independent of frequencyband. That is, any of these applications might be used in any frequencyband, including, but not limited to, the following:

-   -   a) Cellular (800 MHz band)    -   b) PCS (1800 and 1900 MHz bands)—(Personal Communications        Service)    -   c) GSM (900 and 1800 MHz bands)—(Global System for Mobile        communications)    -   d) MMDS (2500 MHz band)—(Multi-channel Multipoint Distribution        Service)    -   e) LMDS (26 GHz band)—(Local Multipoint Distribution Service)    -   f) Bluetooth Applications (2400 MHz band)—(Bluetooth is the name        of a wireless protocol standard, created by Ericsson)    -   g) Indoor Wireless LANs (2400 MHz band)—(Local Area Network)    -   h) 3G (3rd Generation PCS systems) at 1900 MHz (U.S.) and        1800-2200 MHz (Europe)

If it is desired to increase the wide-angle coverage of the signalsre-transmitted by the repeater, one side of the repeater may be providedwith multiple antennas oriented in different directions.

FIG. 24 shows a block diagram of one path through a repeater system. Theinput signal, S(t), either from the base station (for the downlinkpath), or from the mobile user (for the uplink path), is received via anantenna 120, bandpass filtered at 126 a, amplified at 128 (with activegain=G), filtered again at 126 b, and finally transmitted by an antenna122. Some of the transmitted signal energy couples back (through space,or through the electronics) into the receive antenna. This is denoted inFIG. 24 as the feedback signal, f(t), which is simply a delayed version(attenuated) of the original signal, S(t). Therefore, the compositesignal, S(t)+f(t), is fed into the amplifier, with output G(S(t)+f(t)).Assume, for example, that the antennas have 0 dBi gain, then the newfeedback signal is G f(t). The propagation of this signal, back to theinput antenna, will incur attenuation, H. Therefore, the amplified,attenuated signal at the input antenna will be H G f(t). If this signalis comparable in power to the original signal S(t), then the amplifier128 will go unstable, and oscillate (ring). This oscillation will causesevere distortion in the desired signal.

FIG. 25 shows the same circuit as FIG. 24; however, adding an adaptivecancellation circuit 140. The goal of this circuit 140 is to create ainverse f(t) signal−f(t) (a 180 degree shifted f(t) signal), and sum itwith the input signal, including the feedback signal, f(t), at a summingjunction 145, and thereby remove the feedback signal f(t).

FIG. 26 shows a general block diagram (high level) of one form of theadaptive cancellation circuit 140. In this approach, the input (RF)signal is summed at the junction 145 with a modulated signal constructedvia a digitally adaptive process, to destructively interfere with thefeedback signal embedded in the input composite signal. After thesummation, the composite signal, S(t)+f(t), is digitally sampled anddigitally processed via a digital signal processor (DSP) 150, whichcomputes an intermediate signal for a modulator 152. The modulator 152takes the intermediate signal, and a sample of the amplified (output)signal, and creates a near copy of the correct inverted f(t)signal−f(t). This process will work with many, if not most, of thedigitally adaptive algorithms for feedback control. Additionally, thismethodology does not require an injected signal (training or pilot tone,or wideband noise), for the adaptive process.

FIG. 27 shows the circuit 140 in further detail. The DSP 150 is acombination of an RF downconverter 160 to shift the signal to anintermediate frequency that allows digital sampling, ananalog-to-digital (A/D) converter 162 which digitizes the analog signal,and a processor 164 which performs the required operations to computethe intermediate signal. The modulator 152 is a combination of acontrollable attenuator 166, and an I/Q modulator 168. Additionaldetails shown in FIG. 27 include respective couplers 172 and 174 whichcouple the signals from the signal paths to and from the adaptivecancellation circuit 140, a first coupler 172 being interposed betweenthe summation junction 145 and the filter 126 and the second coupler 174being at the output of the power amplifier 128. In addition to thecouplers 172 and 174, respective delay lines 182 and 184 may be employedat either end of the RF path, one just prior to the summing junction 145and one subsequent to the coupler 174.

FIG. 28 shows a block diagram of a repeater system using adaptivecancellation (AC) circuit 140, details of which are shown in FIGS. 26and 27. The “direction” of the circuit 140 in each RF path has beentaken into account. In this system, each (uplink, downlink) path has aseparate AC circuit block 140, and the system uses diplexers 130 becauseit has only one antenna on each side of the repeater.

FIGS. 29 and 30 show the directional characteristics of the AC circuitblocks 140, whether for the downlink or uplink path. The blocks are“mirror images” of one another, differing by the direction of thedesired signal, with the arrows 175 denoting the directionality of eachcircuit 140.

FIG. 31 shows a side-to-side repeater 190 having a body or housing 192having opposed flat surfaces. To each of these opposed flat surfaces,there is mounted a single patch antenna element 194, 196, respectivelycomprising the antennas on the mobile-facing side and thebase-station-facing side. An equivalent circuit diagram is shown in FIG.32. It will be understood that the circuit components of FIG. 32,including the adaptive cancellation (AC) circuits, may be carried in thebody or housing 192.

Similarly, FIG. 33 shows a side-to-side repeater 190 a having a similarbody or housing 192 a which mounts separate uplink and downlink transmit(Tx) and receive (Rx) patch antenna elements for each of the twoantennas. The respective Tx and Rx antennas on one side of the repeaterare designated by reference numerals 194 a and 194 b, while therespective Tx and Rx antenna elements on the other side are designatedby reference numerals 196 a and 196 b. The circuits shown in FIG. 34 maybe mounted to (in) the body (housing) 192 a.

As indicated above, the electronics, including the adaptive cancellationcircuits, may be carried on/in the body/housing 192, 192 a of theantenna element in the side-to-side repeater structures of FIGS. 31 and33, permitting a tower-top modular repeater installation, in addition tothe other advantages

As indicated above, FIGS. 31 and 32 show the case for a single antenna(element) on each side, including frequency diplexers to separate eachpath (or frequency band). FIGS. 33 and 34 show the approach when usingseparate Tx and Rx antennas, and therefore separate circuits, for each(uplink, downlink) path.

The above-described approach may be used in a number of applications,including: Cellular Coverage (null fill, in-building systems), PCS,MMDS, WLL and LMDS.

FIG. 35 illustrates a typical prior-art repeater implementation 215residing on a mast or tower 220 and including a base-station-facingantenna 222 for exchanging signals with a base station 224 at a remotelocation. The base station 224 may include a tower 226, transmit andreceive antennas 228 and base station equipment 230. A mobile-facingantenna 232 exchanges signals with the subscriber which may be a mobilesubscriber as illustrated by an automobile at reference numeral 234. Theantenna 232 may be designed, located and installed so as to providecoverage over a null fill area 236, as will be described below. Theantennas 222, 232 are coupled with the repeater electronics 225 which ismounted elsewhere on the mast or tower 220 by runs of coaxial cable 227,229.

Referring now to FIG. 36, a repeater implementation in accordance withone embodiment of the invention is designated generally by the referencenumeral 245. Similar to the arrangement in FIG. 35, the repeaterequipment is mounted to a mast or tower 220 and has abase-station-facing antenna 222 and a mobile-facing antenna 232. Similarto the arrangement in FIG. 35, the antenna 222 communicates withantennas 228 at the base station 224, and the antenna 232 communicateswith user equipment which may be a mobile unit 234 with coverage beingprovided in a null fill area 236. Departing from the prior art, therepeater of the invention comprises an integrated repeater system inwhich the repeater electronics 225 are incorporated into a single unitor module 250 along with the two antennas.

Often a major challenge for wireless service providers is getting accessto an equipment site situated in an optimum location. As shown in FIG.37, the direction from the base-station-facing antenna 322 of therepeater to the base station 324, and/or the direction of themobile-facing antenna 332 to the null site 336 (i.e., the null fillarea) is rarely at a right angle to the face of the donor or nullantenna. In fact, this angle will vary significantly from site to site.To address this problem, one embodiment of the invention uses an antennaarray with a beamformer network that can be programmed, e.g., from alook-up table. This allows the two antennas to be beam-steered towardthe location of the base station and null sites.

The antennas and beamformer can be implemented in several ways. Theblock diagrams in FIGS. 38 and 39 show two possible implementations.FIG. 38 is an implementation that uses a common antenna for transmit andreceive on each side of the repeater. FIG. 39 shows separate transmitand receive antennas 322 a, 322 b and 332 a, 332 b on each side of therepeater. The implementation of FIG. 38 uses duplex filters or diplexers360, 362 to separate the downlink path and uplink path signals forprocessing by the repeater. This approach has the advantage that thetotal area on the side of the integrated repeater 350 can be utilized toaccommodate a larger antenna array. However, this approach requires thatthe filters 360, 362, provide all of the isolation between the downlinkpath and uplink path of the repeater. FIG. 39 is an implementation thatuses separate transmit (332 a, 332 b) and receive (322 a, 322 b)antennas and filters 400, 402, 406 a and 406 b. This approach also hasthe advantage of using the isolation of the two antennas to reduce thefiltering requirements in the repeater. However, this approach mayincrease the area required for the antennas on the sides of therepeater.

The remaining repeater circuits may be implemented in a number of ways.The embodiments shown in FIGS. 38 and 39 use a channel-selectiveapproach. In this approach, a Low Noise Amplifier (LNA) 390 amplifiesthe low-level signal from each of the antennas, and is a very quietamplifier to ensure that a good signal-to-noise ratio is maintained inthe repeater. After the LNA 390, the desired signal moves to a channelmodule, comprising an uplink channel module 394 in the uplink path and adownlink channel module 396 in the downlink path. In the channel module,the desired signal is downconverted to a lower intermediate frequencyand filtered to limit the spectrum amplified by the repeater to a singlechannel or set of channels. The intermediate frequency is thenupconverted back to the original frequency of the desired signal. Theoutput signal of the channel module is then routed to a power amplifier398 in each path to create a high level transmit signal. In FIG. 39,respective filters 400, 402 are provided between the LNA's and PowerAmplifiers and associated beamforming and selection circuits 404, 406(to be described below) for the donor and null antennas. Interferencecancellers 408 are connected between the outputs of the power amplifiersand the inputs of the LNA's.

The invention may use a direct RF, offset RF, DSP, or GPS based repeaterinstead of the above-described channel-selective approach. Examples ofDSP and GPS repeaters are shown respectively in copending U.S. patentapplication Ser. No. 09/460,023, filed Dec. 13, 1999 and Ser. No.09/513,543, filed Feb. 25, 2000, which are incorporated herein byreference. A direct RF repeater performs all gain and filteringfunctions at the high frequency of the desired signal. An offset RF orfrequency translating repeater is similar to a channel-selectiverepeater except that the upconversion of the intermediate frequencymoves the signal to a new high frequency signal instead of the originalfrequency of the desired signal. This approach will minimize oreliminate the need for an interference canceller. A DSP repeater willstill utilize an LNA and power amplifier, but the processing functionsin the channel module are handled by digitizing the desired signal,performing the function digitally and then converting the digital signalback to an analog signal.

As shown in FIGS. 40 and 41, the antennas 322 and 332 can be implementedusing antenna arrays 370, 380. Each antenna array uses a row of Mhorizontally spaced elements to achieve the desired azimuth beamwidthand N vertically spaced rows of elements to achieve the desiredelevation beamwidth. This invention may use many different types ofantenna elements in the antenna array. Some examples include patchantennas 372 (FIG. 40) and bow-tie dipoles 382 (FIG. 41). FIG. 40 is anexample of a patch antenna array 370 with M=4 and N=3. FIG. 41 is anexample of a bow-tie dipole array 380 with M=4 and N=2.

The beamforming and selection networks 404, 406 and 404 a, 404 b, 406 a,406 b in FIGS. 38 and 39, combine the antenna elements 372 or 382 in theantenna array 370 or 380 with appropriate phase and amplitude to createthe desired antenna pattern. Several methods can be used to implementthe beamforming and selection networks. One method of implementing thisis to use a M×N Butler matrix to perform the phasing and combiningfunctions. The angle and elevation of each beam is stored in a look-uptable that the repeater uses to drive a diode or relay switch matrix toselect the desired beam. This look-up table is stored in a memory of therepeater controller 410 in order to map the desired azimuth and programother parameters and matrix settings for use by the Butler matrix.

One example of a Butler matrix for beamsteering is shown in FIG. 45.Here a plurality of antenna elements 800 are arranged in a 3 by 3 array.The antenna elements 800 may be patches 372 such as in FIG. 40, dipolessuch as the dipoles 382 shown in FIG. 41 or another form of antennaelements. All the antenna elements 800 in the array are coupled with atwo-dimensional Butler matrix 802. The two-dimensional Butler matrix 802is in turn coupled with an M:1 radio frequency (RF) switch 804. In theillustrated embodiment, M=9, the total number of antennas 800 in thearray coupled with the Butler matrix 802. The RF switch 804 iscontrolled by a controller or control circuit module 806 via a controloutput 805 which may also control other similar RF switches for theother repeater antenna array via an additional control output 807 asshown in FIG. 45. The controller 806 may be a part of the controller 410of FIG. 38 or 39.

The controller 806 may be set to sequentially switch to the beamsprovided by the antenna 800 via the Butler matrix 802 and RF switch 804to search for an optimal signal, such as the highest net power output.This is indicated in FIG. 45 by an RF connection 808 from the output ofthe switch 804 to an input of the control circuit 806 for monitoring theRF output. Other parameters might be used to control switching such asthe lowest noise or some other measure of signal quality. Thus, inoperation, the control circuit 806 switches antenna elements until an“optimum” signal output is located and then remains connected to theantenna element at which the optimal signal is received. RF circuitssimilar to that shown in FIG. 25 are located between the switch 804 anda similar switch (not shown) which is coupled in the same fashionindicated to a similar Butler matrix to select a beam from a similarantenna array (not shown) at the opposite side of the repeater. Thecontrol module 806 similarly controls this second RF switch coupled withan antenna array at the other side of the repeater via a control line807. The second RF switch may be controlled by the control circuit 806on the same basis, for example, on the basis of signal strength or someother measure of signal quality. The RF circuit includes respectivediplexers 809 (where the respective antenna elements 800 perform bothtransmit and receive functions), power amplifiers 810 and filters 812.

A system of beamforming or beam selection other than a Butler matrix mayalso be utilized without departing from the invention. For example, thesignal processor or controller 410 (e.g., in FIG. 38 or 39), in additionto its other functions, can be programmed and adapted to perform acontinuous variable, essentially linear beamforming function bycontinuous adjustment of the N beams coming in with a variable phase andamplitude weighting being applied, to develop a single beam direction tocorrespond to the desired beam direction of either of the antennas forcommunicating with a base station or subscriber equipment. Various phaseand amplitude settings can be prestored for a number of beams, forexample N beams, each with a given directional characteristic orsetting, from which the processor chooses the best match for a givensituation.

Another method is to build the phasing and combining networks withvariable phase devices in series with each antenna element. A look-uptable of phase values for discrete angles and elevations is then used tocreate the desired beam. In FIG. 46, the antenna elements 800 in an N byN (e.g., 3 by 3) array are each coupled with a respective one of aplurality of phase shifters 820. The phase shifters are in turn coupledvia a corporate feed 822 to an RF output A which may couple with the RFcircuits as shown in FIG. 45. A controller 824 is provided to controlall the phase shifters 820. The same arrangement is utilized for theantenna on the opposite face of the repeater.

The latter arrangements differ from the Butler matrix in that only onebeam or directional output is developed or generated for a givenrequirement or situation or relative location. In contrast, in theButler matrix, a total of N beams are available at all times with aswitching network being utilized to select the one of these N beams bestsuited for a given situation or placement of the repeater tower relativeto the base station and null fill area, respectively.

FIG. 47 illustrates the flat-panel approach to repeater constructionusing arrays of antenna elements. For relatively low power applications,a first face 822 a may mount a plurality antenna elements 800 which maybe patches, dipoles or other antenna elements. Similar antenna elementsmay be mounted in an array on the opposite face 832 a. The relativelythin housing 852 a between the two faces or surfaces 822 a and 832 a mayhouse the electronics.

Referring to FIG. 48 in an alternate design, each of a pair of flatpanels 850 b and 850 c mount antenna elements (not shown) only on theiroutwardly facing surfaces 822 b and 832 b. The two panels 850 b and 850c are pivotally mounted to a pair of brackets 850, 852 or other supportstructure at pivot points 854 and 856 and aligned pivot points (notshown) at the bottom edges of the respective panels 850 b and 850 c. Aseparate electronics housing or enclosure 852 b may be coupled with thebrackets or other support structure 850 and 852 intermediate the twoflat panels 850 b and 850 c. The beamsteering may be accomplished bytilting (or rotating) the respective panels until the maximum signalstrength, or some other measure of signal quality is achieved.

FIGS. 49 and 50 are simplified diagrams illustrating beamsteering viathe use of various delay lengths by using striplines of differentlengths on different layers of a multi-layer printed circuit boardselectable by an RF switch (FIG. 49) or striplines of different lengthsprinted on the same circuit board and selectable via RF switches (FIG.50). Thus, in FIG. 49, antenna elements 480, 482 and 484, 486 are eachcoupled to multiple striplines of different lengths, represented byvarious solid and broken lines designated generally by the referencenumeral 488. All these lines 488 of various lengths are coupled togetherat radio frequency (RF) summers 481. That is, all of the lines 488 of afirst length are coupled to one summer 483, all of the lines 488 of asecond length are coupled to a summer 485, and so forth. A radiofrequency (RF) switch 487 operated in response to a control signal on acontrol line 489 selects from among the lines of different lengthsconnecting the various antenna elements 480 to the summers 483, 485,etc. The control signal may be produced automatically in response to ameasurement of signal strength or some other optimal signal quality, inorder to accomplish beamsteering via the selection or adjustment ofstripline length.

In the approach shown in FIG. 50, the selection of striplines 490 ofvarying length is accomplished at the antenna elements 492, 494, 496,etc. by respective radio frequency switches 491, 493 and 495. All thesedelay lines of varying length feed a common RF output 497. The delayline length for each antenna may be selected either independently or inunison with the selection of delay lines for other antennas, in responseto suitable control signals (C) in much the same fashion as in FIG. 49,and/or, as described above, in response to detection of an optimalsignal level or some other optimal signal quality measurement.

Typically, a repeater site uses the physical separation of the antennasto achieve enough isolation to allow the repeater to operate with gainsof 60 to 95 dB. Because the antennas are located relatively closetogether in the flat-panel repeater, another approach is needed toachieve isolation. As described above, such an approach can include theuse of radio frequency chokes in the enclosure between the antennas toreduce the coupling between the antennas, or the use of an adaptiveinterference canceller to provide additional gain and phase margin, asdescribed above.

A limiting characteristic for repeaters is that of the feedback loop, orconversely, the isolation between the two opposing antennas (orsensors). That is, the total front to back (F/B) ratio for the system,or isolation, must be higher than the desired gain. Generally speaking,the isolation between donor and null antennas is equal to the totalrepeater gain plus some margin, typically around 10 to 15 dB. Therefore,the repeater gain will in general be less than the isolation minus themargin. For example, if the isolation between antennas is around 60 dB,then the maximum repeater gain allowed will be about 45 dB. For PCSfrequencies, these figures may result in a repeater range of less than100 feet.

In a scattering environment, which is common in PCS, every 6 dB ofadditional system gain will double the coverage distance. Thus,obtaining an additional 24 dB of isolation between the two antennas,will allow the range to double 4 times, to 1600 feet. For conventionalrepeater systems as in FIG. 35, where the two antennas and repeaterelectronics are in three separate enclosures, and locations, the donorantenna (to the base station) and null antenna (to the desired coveragearea), are separated in space by (usually) more than 10 feet. Thisdistance adds over 50 dB to the isolation between antennas, generating atotal isolation value of well over 100 dB. Therefore, with a 15 dBmargin, this type of system can utilize a total gain of up to 85 dB ormore, which results in fairly large range and coverage.

For the integrated repeater of this invention, where the opposingantennas are in or on the same housing or enclosure, and separated inspace by as little as a few inches, isolation is typically limited to avalue below 80 dB or so. This therefore allows a total repeater gain ofno more than 65 dB, which may limit the system range to a few hundredfeet or less.

The adaptive cancellation approach removes a significant portion(between 10 dB and 40 dB) of the feedback signal power, thereforeincreasing the total system isolation by the same amount (10 to 40 dB).This additional isolation can be used to achieve greater repeater gain,and therefore significantly extend the range of the system. This isespecially useful in the integrated repeater.

Isolation between the two sides of the repeater can also be improved bythe use of different sized arrays of antenna elements on the mobile andbase station sides to reduce the effect of multipath interference anddecrease direct coupling between the two antennas. Thus, an N×M array ofdipoles on the base station side of the repeater may be sized to providehigh gain and a directive beam to limit reflections from nearby objectssuch as walls and ceilings. For example, a 2×2 array might be used. Thearray spacing may be chosen as a half wavelength at the center frequencyof the frequency band being amplified and re-transmitted by therepeater, to produce a null in the array factor on the horizons, thusreducing the direct coupling between the antennas on opposite sides ofthe repeater. For the broader beamwidth desired on the other side of therepeater, to provide a large coverage area, a linear array of N dipolesmay be used. This linear array produces a fan beam with increaseddirectivity in the elevation plane, which acts to reduce the multipathinterference due to reflections from nearby objects such as walls orceilings. The dipole arrays are preferably implemented as twin-line-feddipoles with tuning stubs for impedance matching. A coax-to-twin-linebalun may be implemented with a smooth transition from a microstrip lineto a twin line on the same substrate as the antenna and corporate feed,resulting in a compact, low-cost antenna. The dipoles are preferablypolarized at a 45° slant for optimum reception of signals of unknownpolarization, with opposite slants on opposite faces of the repeater formaximum isolation. As an alternative, antenna elements may be providedon opposite sides of the repeater to produce circularly polarizedradiation patterns, preferably of opposed polarities.

The microprocessor or controller (repeater controller) 410 provides therepeater control functions. This controller provides all setup,communications, and monitoring functions for the repeater. Thesefunctions include those related to setting the beamforming and selectionfunctions to the desired beam, as mentioned above, and setting theamplifier gain and frequency of operation to the maximum usable gain forstability and the power rating of the repeater.

The controller's functions may also include monitoring of power levelsat various points in the system, monitoring of the status of the devicesin the system, for example for over-power, under-power, oscillation,etc. The controller may also include communication ports forcommunication with outside devices. For example, a local connection,such as an RS-232 port may be provided to communicate with a laptopcomputer which may be used in the field to exchange data with thecontroller, update data or program routines, or the like. A remotecommunication port or protocol may also be employed to enablecommunications with a network management system, through a localtelephone company or wireless serial communication port, such as a datamodem or TCP/IP (Transmission Control Protocol/Internet Protocol) orSNMP (Simple Network Management Protocol). In this regard the controller410 may comprise a microprocessor with a UART (Universal AsynchronousReceive Transmit) to enable the desired communications and commandstructures and protocols.

FIGS. 42 and 43 are software flow charts for the initialization of therepeater, which includes beam selection on the base-station-facingantenna and the mobile-facing antenna and the initial gain settings. Theblocks in the flowcharts of FIG. 42 and FIG. 43 are as follows:

Reference No. Function 500 Power On/Reset 502 Disable Repeater 504 GetDonor Site Coordinates & Elevation 506 Get Null Area Coordinates &Elevation 508 Get Repeater Site Coordinates & Elevation 510 Get CompassDirection of Repeater 512 Calculate Pointing Angle to Donor 514 GetDonor Beamformer Settings From Look-Up Table 516 Set Donor Beamformer518 Calculate Pointing Angle to Null 520 Get Null Beamformer Settingsfrom Look-Up Table 522 Set Null Beamformer 524 Set Repeater Gain toMinimum 526 Set Repeater Channel Frequency 528 Enable Repeater 530Measure Forward Power 532 Forward Power Over Limit? 534 Display Warning536 Disable Repeater 538 Increase Gain 6 dB 540 Measure Forward Power542 Forward Power Over Limit? 544 Forward Power Increase 6 dB? 546Decrease Gain 6 dB 548 Decrease Gain 6 dB 550 Go to Main Loop 552 End

FIG. 44 is a software flow chart for a main operational loop of therepeater control program, and includes only the functions related toauto gain control of the repeater. The blocks in the flow chart of FIG.44 are as follows:

Reference No. Function 600 Main Loop 602 Wait Time T1 604 MeasureForward Power 606 Forward Power Over Limit? 608 Decrease Gain 2 dB 610Increase Gain 2 dB 612 Measure Forward Power 614 Forward Power Increase2 dB 616 Decrease Gain 2 dB 618 Decrease Gain 4 dB

The automatic gain control feature may also be used to monitor undesiredfeedback and adjust the gain of the appropriate signal amplifier(s) toprevent oscillation. An oscillation detector may also be included tomonitor the current flow through the amplifier and produce a signal thatcan be used to shut down the repeater, or the appropriate circuits inthe repeater, in the event that oscillation actually occurs.

FIG. 51 shows a solar panel 910 with a battery 911 on a relatively thin,flat antenna 912 of the type described above. The addition of a “solarpanel with battery” system allows the repeater to be installed in alocation with sunlight, and therefore mitigate the requirements for anexternal (DC) power source. The system actually operates from thebattery unit, which is occasionally (when the sun is up) re-charged fromthe embedded solar panel unit. This is an excellent application for spotcoverage requirements for a repeater, where there is currently not alocal power source or wiring. Additionally, it aids the installation ofthe unit indoors (assuming sufficient lighting, to recharge thebatteries, where there is no local power plug). Lastly, it is moreaesthetic, than requiring wire runs to the unit. Note that the solarpanel can be on the top, sides, and/or the front face (with a hole forthe patch antennas). The battery system is inside the unit; adjacent tothe RF hardware (amplifiers, etc.).

In order to improve the front-to-back isolation between the two antennasof the repeater, the two antennas can also be physically separated fromeach other by a distance of at least several feet, as illustrated inFIG. 52. For example, separating the antennas by only 10 feet equates toa 40-dB propagation loss in the PCS frequency band. In FIG. 52, twoseparate antennas 921 and 922 of a repeater are mounted on the walls 923and 924 at opposite ends of a room or space within a building and areinterconnected by a coaxial cable 925 extending along or within theceiling 926.

In FIG. 53, two separate antennas 931 and 932 are mounted on oppositesides of an exterior wall 933 of a building and are interconnected by acoaxial cable 934 extending through the wall 933. FIG. 53 a illustratesan H-shaped repeater housing 935 that eliminates the need for thecoaxial cable 934 in FIG. 53, and FIG. 53 b illustrates aninverted-U-shaped housing 936 that accomplishes the same result. FIG. 53c illustrates a repeater housing 937 having a central section that notonly spaces the two sides of the repeater from each other, but also isshaped to fit over a pole P to facilitate both the mounting of therepeater and the orientation of the antennas on the opposite faces ofthe repeater. That is, the repeater 937 can be simply rotated around thepole P to the desired angular position. FIG. 53 e illustrates anotherform of inverted-U-shaped repeater housing 938, and FIGS. 53 f and 53 gillustrate two modified housing structures 939 and 940 adapted to bemounted on a pole P. The housing 939 comprises two sections joined by acoaxial cable 939 a.

FIG. 54 illustrates an embodiment in which a pair of diplexers D1 and D2and an amplifier A are integrated with each of the two antennas 941 and942 for simultaneous transmission of bidirectional signals between eachantenna and a common interconnecting coaxial cable 943. Alternatively,all the electronics can be integrated with just one of the antennas tofurther simplify the hardware and reduce the number of diplexersrequired.

Instead of connecting the physically separated antennas via coaxialcable, the physically separated antennas can be coupled wirelessly,using either RF or infrared wireless coupling. The signals arriving atthe two antennas from outside the repeater are converted to a differentfrequency for the local transmission between the two antennas within therepeater, to avoid interference with signals within the system band andthereby improve the total system gain.

Referring to FIG. 55, within a repeating device 1010, individual lowgain amplification devices (e.g., negative resistance amplifiers 1012,1014) that separate input and output signals by their direction ofpropagation can be connected in circuit with directional antennas 1016,1018 to provide low gain, short range repeating devices or “repeatingcells” 1010. In FIG. 56, numerous such repeating cells 1010 are arrangedin a parallel fashion within a repeater 1020 such that in the directionof propagation, the signals of all the devices add. Thus, the total gainof the repeating device 1020 is the additive gain of all the individualrepeating cells 1010. This device includes a pair of repeaters 1020 and1020 b, each constructed of multiple cells 1010 of the type shown inFIG. 55. The two repeaters 1020 and 1020 b may be connected in a “daisychain” configuration, with one repeater 1020 passing a signal to and/orreceiving a signal from the other repeater 1020 b. In practice, thesetwo repeaters are located considerably farther apart than indicated inthe somewhat simplified diagram of FIG. 56.

In each cell 1010, a hybrid coupler 1015 (FIG. 55) functions to separatethe incoming signal from the outgoing signal. Filters 1022 and 1024 arealso provided between the hybrid coupler 1015 and the antennas 1016 and1018, respectively. The practical isolation of the hybrid coupler is15-20 dB, which limits the maximum gain of the negative resistanceamplifier to 6-15 dB. Useful repeater range typically requires 50 to 60dB total gain. The directive antennas 1016, 1018 can provide 19 dB gaineach, and thus each cell can have a gain of as much as 53 dB (19+19+15).Accordingly, the construction of a repeating device or repeater using aplurality of such cells in parallel is capable of providing considerablegain.

Moreover, it is possible to construct an individual cell of thegeneralized configuration of FIG. 55 with adequate repeater gain to meetthe typical gain requirements of a useful repeater. The antennas 1016,1018 can each be a 16 element (4×4) flat-panel array. Based on thisapproach, FIG. 57 shows one embodiment of the invention in which therepeater 1020 is configured in the form of a rectilinear box housing1030, having opposed square (or rectangular) faces 1032 and shorterconnecting sidewalls 1036, 1038. Radiating elements, such as a patchelement 1016 for each cell 1010, are arrayed on faces 1032. The specificshape of the housing may be different from that shown.

Referring now to FIG. 58, a repeater diversity system in accordance witha further aspect of the invention is employed in a repeater system 1110mounted on a tower 1112. At the top end of the tower 1112, amobile-facing antenna 1114 and a base-station-facing antenna 1116 aremounted facing in generally opposite directions. Appropriate feeds suchas coaxial cables or other suitable feedlines 1118 and 1120 respectivelyrun from the antennas 1114 and 1116 to an electronics enclosure 1122located at a lower part of the tower 1112, in which therepeater-associated electronic circuitry is located, which circuitrywill be further described in connection with FIG. 59. The antenna 1114generally broadcasts and receives signals relative to a remote userlocation or subscriber equipment. This subscriber equipment may bemobile equipment such as in a cellular or PCS system, or the like. Thus,the signal source received by the antenna 1114 from the remote equipmentmay be a mobile signal source. The antenna 1116 transmits and receivessignals relative to a base station at some remote location. The repeaterelectronics 1122 boosts the signals as they are passed between the twoantennas, to enhance the communications between the remote source andthe base station.

As shown in FIG. 59, the antenna 1114 includes a main antenna 1130 and areceive (Rx) diversity antenna 1132. In one embodiment, these twoantennas 1130 and 1132 are arranged to have the same phase center butmutually orthogonal polarizations (see FIG. 61). By using thisarrangement, the problem of location-induced phase variation issubstantially eliminated. This fact can be used to overcome thecomplications in differential phase variation of the main and diversitysignals of a mobile signal source, when the signal source is moving overtime relative to the repeater location.

In the illustrated embodiment, the main mobile-facing antenna 1130 andthe base-station-facing antenna 1116 serve to both transmit and receivesignals relative to the remote or subscriber equipment and the basestation, respectively. Accordingly, each of these antennas is providedwith a frequency diplexer 1140, 1142 to accommodate the use of differentfrequency bands in the uplink and downlink channels.

Referring first to the uplink channel 1150, it will be seen that thereceive signals from the main and Rx diversity antennas 1130, 1132 arefed through respective low noise amplifier (LNA)/attenuator circuits1152, 1154 and combined at a combining network 1156. In one embodimentthe combining network combines these signals with a fixed phaseadjustment. The incoming signal from the Rx diversity antenna 1132 isinitially processed by a suitable filter 1158. The combined signal fromthe combining network 1156 is further processed by an uplink channelmodule 1160, amplified by a power amplifier 1162, and fed to the donorantenna 1116 via its associated diplexer 1142. In accordance with oneembodiment of the invention, the signals from the main and Rx diversityantennas 1130, 1132 are combined at the combining network 1156 withequal gain from the low noise amplifiers 1152, 1154. In the illustratedembodiment, the signals from the antennas 1130 and 1132 are aligned inphase by the combining network 1156 and uplink channel module 1160, inaddition to being combined with equal gain settings on each path.

Completing the electronics 1122, a downlink channel module 1170 receivessignals transmitted from the base station via the antenna 1116 and itsassociated frequency diplexer 1142, which signals are first amplified bya low noise amplifier (LNA)/attenuator 1172. The output of the down linkchannel module 1170 is fed through a power amplifier 1174 to thediplexer 1140 for transmission by the main antenna 1130.

Typically, each channel module includes an upconverter, a filter, and adownconverter. Some gain may also be provided. Suitable channel modulesare made by Andrew Corporation, the assignee.

In the system of the invention as described above, the two antennas 1130and 1132 provide two separate versions of the receive signals from theremote or subscriber equipment with statistically independent multipathcharacteristics, since the vertical and horizontal field components in acommunications link are highly uncorrelated. By using receive antennas1130, 1132 that have the same phase center and mutually orthogonalpolarizations, differential phase variations induced by the changinglocation of a mobile remote source are substantially eliminated. Thisovercomes the usual challenge of equal gain combining which requiresthat the two diversity paths be aligned in phase, since phase alignmentwould normally be made difficult by the changing location of the mobilesignal source.

Advantageously, the invention makes possible the implementation ofreceive diversity in a repeater being used in a wireless communicationsystem. The implementation of receive diversity in a repeater is notlimited to a single type of system (e.g., CDMA) but could be implementedfor any digital-or analog-based wireless communications system. Theinvention provides, on average, a 2.5 to 3 dB increase in the averagecarrier-to-noise ratio of the received signal.

Rather than a single main mobile-facing antenna and a signalbase-station-facing antenna as described above, with frequencydiplexers, the repeater may employ separate transmit and receiveantennas on both sides, utilizing separate signal paths in amplificationtherebetween. Such an arrangement is shown in FIG. 60. In this case, thesignal from the main receive antenna 1130 a combined with the signalfrom the receive diversity antenna 1132 at the combiner 1156, afterbandpass filtering at filters 1140 a, 1158 and equal gain amplificationat LNA's 1152, 1154.

In the case of separate transmit and receive base-station-facingantennas, an LNA 1172 receives signals from the antenna 1116 b which ittransmits through a down link channel module 1170, power amplifier 1174and bandpass filter 1140 b to the antenna 1130 b. Similarly, the mainmobile-facing receive antenna 1130 a delivers received signals to an LNA1152 (after bandpass filter 1140 a), which, upon being combined withsignals from the Rx diversity antenna 1132 at a combining network 1156and processed at an uplink module 1160, are delivered via a poweramplifier 1162 and transmit bandpass filter 1142 a to a transmit antenna1116 a for transmission to the base station.

In one specific example of a CDMA repeater system, the uplink module1160 employs a channelizer having a gain of about 24 dB or greater foran uplink path channel in a frequency range from 1850 to 1910 MHz.Similarly, the downlink module 1170 utilizes a channelizer having a gainof at least 24 dB for a downlink path channel in a frequency range of1930 to 1990 MHz. In this embodiment, the gain of the low noiseamplifiers 1152 and 1154 is 33 dB or greater, and the gain of the poweramplifiers 1162 and 1174 is 43 dB or greater.

FIG. 62 is a block diagram showing the use of a typical RF Butler matrix1220. These devices are used in analog communication to generatemultiple antenna beams, from a composite antenna system having aplurality of antenna elements 1222. Butler matrices can be purchasedcomplete, or generated from a composite circuit of 90 degree hybrids andRF summer circuits. In FIG. 62, a total of M antennas, each with similarcharacteristics, are used as the input to the Butler matrix. The Butlermatrix device then generates K unique RF (analog) outputs 1224, each fora respective beam direction.

Equation (1) below is a general empirical equation (model) for anM-point Discrete Fourier Transform (DFT). This type of transform isnormally used in digital technologies to derive the frequency response,X(k), for a series of time domain inputs, x[i]. For example, a FastFourier Transform (FFT) is simple a radix-2 DFT. Thus, the FFT (or DFT)transforms the time domain response into a frequency domain response.

$\begin{matrix}\begin{matrix}{{X(k)} = {\frac{1}{M}{\sum\limits_{i = 1}^{M}\;{{x\lbrack i\rbrack}{\mathbb{e}}^{{- {j(\underset{\pi}{2/M})}}{k{({i - 1})}}}}}}} \\{j = \sqrt{- 1}}\end{matrix} & (1)\end{matrix}$

Similarly, the Butler matrix acts as a transform from the spatialresponse, x[i], to the sectored (or beam) space response, X(k).

FIG. 63 shows an example of a beam pattern for one of the spatialelements (or antennas) 1222 from FIG. 62. Each antenna has a 120 degreesector beamwidth, or Half Power Beam Width (HPBW). Thebase-station-facing antenna preferably has a narrower half powerbeamwidth than the mobile-facing antenna. For example, the beamwidth ofthe base-station-facing antenna is typically about 30 degrees, plus orminus 5 degrees, while the beamwidth of the mobile-facing antenna isabout 60 degrees, plus or minus 10 degrees.

FIG. 64 shows four (4) similar antennas 1222 feeding a Butler matrix1220 in a similar configuration to FIG. 63. Each input antenna has asimilar 120 degree HPBW, as shown in FIG. 63. For this case, M=4 inequation (1) above. The Butler matrix is therefore a 4-port device, with4 input ports and 4 output ports. The output ports 1224 in FIG. 64 arelabeled with a numerical designation for the RF output for each beam,corresponding to the numerical designation of the antenna elements 1222at the input ports.

FIG. 65 shows the azimuth beamwidth response for the Butler matrix inFIG. 64. Each beam has a beamwidth equivalent to roughly 120 degreesdivided by four (or M), which is roughly 30 degrees. Additionally, thedirection for each of the 4 output beams is uniformly spaced by about 30degrees. Therefore, the Butler matrix transforms the response of 4 wideangle antennas, all pointing in the same direction (thus all “seeing”exactly the same view), into 4 narrower beams, which collectively givesubstantially the original view.

The Butler matrix can also operate in “reverse,” assuming that theButler matrix components (and RF switch, discussed below) can handle theRF power. That is, so far, the system has been shown operating in thereceive mode, changing spatial responses to beam responses. However, thesystem also can operate in reverse or transmit mode, changing beamresponses to (wider angle) spatial responses. To operate in the transmitmode, the system would need to be capable of handling RF transmit power,and not destroy or “burn up” the RF components.

FIG. 66 shows a simplified view of a PCB (printed circuit board)-mountedsystem 1300 or “planar switched beam antenna.” Here, M antenna elements1322 (shown here as square patches, or microstrip antennas) mounted onone surface of a PCB 1325 are used for the input response. It is assumedthat all M antenna elements 1322 have a similar azimuth response. Eachantenna response, tapped via a coaxial probe, aperture coupling, orother antenna feed mechanism 1323, is directed to an M-port Butlermatrix 1320, shown as block “B” also mounted on the PCB 1325. The M-RFbeam outputs 1324 from the Butler matrix are fed to an M:1 RF switch1326 (shown as block “S”) also mounted on the PCB 1325. The Butlermatrix 1320 and RF switch 1326 could be mounted on a separate PCB ifdesired and in a common housing with the antennas 1322 and PCB 1325. Itis assumed that the final output RF signal, from a given antenna element1322, is the stationary response of the system.

That is, the RF switch 1326 would be externally controlled, andsequentially switch through each of the beams. Some external systemwould monitor or qualify each output to determine the optimal or desiredone, at which point the RF switch would be controlled to select thatrespective antenna element 1322. An RF transceiver or modem 1328 togglesthe RF switch 1326, to each beam, measures the net power output (orother measurement, such as best C/I, or lowest noise, etc.) of each,then selects the beam with the best power (or other measurement, such asbest C/I, or lowest noise, etc.).

This system, if used in both the transmit and receive modes, assumesthat the patch antenna elements 1322, Butler matrix circuits 1320, andRF switch 1326, all have bandwidth covering the entire transmit andreceive signal bandwidths. Thus, the system can operate in bothdirections; converting wide spatial responses into a single selectedbeam (for receive), and transmitting a signal back towards the desireddirection (transmit mode), assuming sufficient bandwidth and transmitpower handling capacity, as noted above.

The array of antennas 1322 could be formed in the vertical plane, togenerate elevation beams, as an alternative to the horizontal array ofFIG. 66, as discussed below with reference to FIG. 77.

FIG. 67 shows a simplified top view of the layered structure of one ofthe patch elements of FIG. 66, showing the patch structure 1322, aground plane 1342 (above the surface of the PCB 1325) with an aperturecoupled iris 1344, and a microstrip transmission line 1323 on the PCB1325, carrying the signal.

FIG. 68 shows a simplified circuit diagram for the RF switch 1326. M RFtransmission lines 1324 are each connected in parallel, via PIN diodes(or other transistor/solid state switching devices, for RF operationalfrequencies) 1350, to a single point. Each PIN diode 1350 is controlledvia a control (C) or bias line 1352; acting as an electronic switchingcircuit. While only two control lines 1352 are shown, there are Mcontrol lines (C) in total, one for each PIN diode 1350. The M controllines 1352 can be operated from a single control line (not shown in FIG.68) by use of a microcontroller (not shown in FIG. 68) or a TTL (binary)logic device (not shown).

FIG. 69 shows a block diagram of a system having components as describedabove with reference to FIG. 66. The control input 1352 to the M:1 RFswitch 1326 can come from an RF to IF transceiver, or from a modem,determined by the beam selection criteria used. A common housing for theantennas 1322, Butler matrix 1320 and RF switch 1326, which may bemounted to one or more PCBs (see FIG. 66) is indicated by referencenumeral 1355.

FIG. 70 shows a block diagram similar to FIG. 69, but with an RF to IFtransceiver (or transverter, as called in MMDS) 1360 added (e.g.,mounted on the same PC board 1325). The RF circuitry block could includethe Butler matrix, the RF switch, and various transceiver components,all on the same PC board as the antenna, or on one or more separateboards, if desired, and in the same housing 1355.

FIG. 71 shows a similar block diagram to FIG. 70, but with the modem1362 added to the system. The modem 1362 would control the M:1 RF switch1326, since it would likely have the most flexible capabilities toanalyze the various antenna inputs (beams), and determine the optimalbeam. All these components may be on one or more PCBs in a commonhousing 1355. The output from the modem could connect to a PC or LAN(not shown) via USB cable, ethernet, or LAN cable 1364.

FIG. 72 shows a simplified perspective view of a physical embodiment ofa planar system (unit) 1300 a, of FIG. 71, with various elements (Butlermatrix “B”, RF switch “S”, Transceiver “T”, and Modem “M”) all withinthe same housing (e.g., a relatively thin rectilinear structure) or onthe same PC board 1325.

In the case where it is desirable to separate the transmit and receivesystems, or if the transmit and receive bands are too far separated, infrequency, to occupy the same antenna elements (or Butler matrixcomponents, or RF switch components), then they can be broken into twocompletely separate systems. Such a system 1300 b is shown in FIG. 73,where a set of transmit mode patches 1322T connects to its own Butlermatrix 1320T and RF switch 1326T, and similarly, for the receive mode, aset of equivalent antenna elements 1322R (in this case, shown aspatches) tuned to the receive band, a Butler matrix 1320R and RF switch1326R. The system input/output is two RF ports 1370T and 1370R. Thewhole system is contained on a single PC board 1325 and/or within asingle housing (i.e., could be on more than one PC board in thehousing).

FIG. 74 shows a block diagram for the system in FIG. 73. There are Mreceive band antenna elements 1322R, and N transmit band antennaelements 1322T. Generally speaking, M can, but does not have to equal N.Additionally, each system has a separate control input 1352R, 1352T forthe respective RF switch. Indeed, this allows selection of differentbeams for the transmit and receive bands. This may be the case if adesired signal is to be received from a given direction, but thetransmitted signal might be sent out in another direction.

FIG. 75 shows the system of FIG. 74 with the addition of an RF to IFdownconverter (or receiver) 1372 for the receive mode, and an IF to RFupconverter (or transmitter/exciter) 1374 for the transmit mode. Thesystem can connect to an external modem (not shown) via coaxial cable(s)or twisted pair transmission line 1376. The system shown here uses asingle cable; which assumes that the transmit and receive band signalsare IF diplexed into a signal cable, from the transceivers.

FIG. 76 shows the system of FIG. 75, and further including an embeddedmodem 1362. The modem 1362 can be, but does not have to be, included onthe same PCB as either or both the antenna system, and/or transceivers.However, it is assumed that the systems shown in each of FIGS. 74-76 arecontained within respective housings 1355, i.e., each of these drawingsshows a system which is contained in its own housing 1355.

FIG. 77 shows a system 1300 c similar to that of FIG. 66, but using Melevation arrays 1390 of antenna elements 1420 in place of an array of Mindividual elements. Each column 1390-1, 1390-2, etc. of antennaelements, which form elevation beams, can be summed, using a parallel orcorporate feed, and input to the Butler matrix 1420. This can similarlybe done for the case of summed azimuth elements, i.e., horizontal arrays(not shown), with switched beams in the elevation plane.

The systems described thus far may utilize PC board technology (planarand thin), with patch or microstrip antenna elements. By design, a patchelement has a real ground plane, and therefore each patch element only“sees” a 180 degree (half hemisphere) view. Thus, the systems shown sofar, are generally “one-sided.” An option to obtain full 360 degreecoverage is to employ two such systems, back to back, to generate aneffective omni-directional system 1300 d, as shown in FIG. 78. These canbe deployed within the same housing (structure). Each system generates abeam input/output; one for the “front” 0 to 180 degree view, and theother for the “back” 180 to 360 degree (azimuth) view. Thus, the systembreaks up the 360 view angle into 2M beams, each with relative beamwidthabout 360/2M degrees. Additionally, the two input/output beam ports canbe connected to a 2:1 RF switch (with control), not shown, to obtainselection of the final (stationary) beam. However, with this approach,the beams in the endfire direction (towards the edges of the PCB) arehighly attenuated (gain), due to the limited view angle for a patchantenna (element).

An alternative method to obtain a full 360 degree view angle is to usedipole (etched) antenna elements 1522, on a PCB 1525, as shown in FIG.79. Each dipole (shown as “bow-tie” dipole elements, which havebroadband characteristics) has a very symmetric azimuth pattern for afull 360 degree coverage. This system does not employ a backplane orground, as do the patches. Similar to the previous designs, this systemuses a Butler matrix 1520 and RF switch 1526, to generate a single RFinput/output port 1570. However, along the symmetry plane of the printedcircuit board (PCB) 1525, the dipoles 1522 have mirror azimuth beams, asshown in FIG. 80. Thus, selection of Beam #1 towards the back, alsoselects Beam #1 towards the front. In the example shown in FIG. 80,there are only 4 states to choose from, and switch 1526 selects twobeams, in summation; one from each side of the symmetry plane.

FIG. 81 shows a typical installation, either in a home or office, withan antenna system 1300 in accordance with any of the embodimentsdescribed above located on a wall, with a cable run 1302 down the wall,to a PC or server 1304.

FIGS. 82 and 83 show an antenna unit 1400, alone, and installed to alaptop computer 1402. Wireless internet systems require large bandwidthsand data rates (over 50 kbps, up to 2000 kbps), much higher thanconventional wireless voice systems (9.8 kbs). To achieve these ratesrequires much higher system gain levels. These gains can only beobtained by either reducing the distance from the base station (orpicocell) to the remote (CPE unit, terminal unit) or by increasing thedirective gains of the base station antenna and/or terminal equipmentantenna. Antenna gain is a function of the physical size of the antenna.Aesthetics and zoning issues limits increasing the size of the basestation antenna (to achieve additional directive gain). Thus, onealternative is to increase the gain of the terminal equipment antenna,which means increasing its physical size. Currently wireless voicesystems (on a handset) use 2″ stub (monopole) omni-directional antennas,with at best 0 dBi of gain. To satisfy the higher data rates, requiresadditional gain of at least 10 dB (20 dB desired).

The RF Switched Beam Planar Antenna described above is a good approachfor this requirement, and is cost effective. This application wouldembed the RF electronics within the antenna 1400, and mount the systemto the laptop unit. The switched beams would continually search for thebest multipath signal, and lock on; transporting this signal to themodem. The envelop of the beams is within an ellipse; with the majoraxis of the ellipse in the directions perpendicular to the faces of theantenna system. Thus, the side (endfire) angles of the system would havemuch lower (reduced) gain. A series of LEDS 1404 or other suitabledisplay elements could be used (shown at the top), which could aid theuser to help orient the unit, to more optimally orient the antenna facestowards directions of greater signal power.

The flat panel antenna 1400 may further have a USB or other suitableconnection 1406 to interface with the laptop computer 1402. The cable orother connector 1406 may also include a power cable to use battery orother power from the laptop computer 1402, or alternatively, on-boardbattery power may be included within the flat panel antenna unit 1400.If desired, the battery used may be a solar powered type of battery.

In the illustrated embodiment, the flat panel antenna 1400 has agenerally L-shaped cross-sectional profile such that the LEDs 1404 orother display elements are readily visible over the top of the laptopcomputer 1402 when the antenna 1400 is installed thereupon, as indicatedin FIG. 83. However, other shapes of the panel 1400 and otherconfigurations and locations of LEDs or other display elements may beutilized without departing from the invention.

The flat panel antenna unit 1400 may be coupled with the case or housingof the laptop computer 1402 by using one or more velcro pads 1408, or“sticky” tape, or the like. Other arrangements of snap-on, snap-offfasteners or other mounting parts or mounting hardware may be utilizedwithout departing from the invention.

The LEDs or other display elements 1404, as well as suitable circuitryfor determining signal strength, or some other desirable measure ofsignal quality may be incorporated in the flat panel antenna 1400, orindeed in any antenna configured in accordance with the invention.

Certain of the flat antennas described above may have azimuth and/orelevation beamwidths of 90° or less, which can restrict or reducecoverage in the end-fire directions. To achieve wider angle coverage,multiple antennas may be used on one or both sides of the flat-panelrepeater. One such embodiment is illustrated in FIG. 84, where arepeater 1500 has a single base-station-facing antenna 1501, and threemobile-facing antennas 1502, 1503 and 1504. The plane of the middleantenna 1503 is parallel to that of the base-station-facing antenna1501, but the planes of the other two antennas 1502 and 1504 intersectthe planes of antennas 1501 and 1503 at angles of about 45° so as toproduce beams that overlap the beam of the middle antenna 1503, asillustrated by the broken lines in FIG. 84. The azimuth beamwidth of themiddle antenna 1503 is typically only about 80°, but the addition of thetwo angled antennas 1502 and 1504 provides wide angle coverage on themobile side of the repeater. FIG. 85 illustrates how an RF splitter 1505can be used to connect all three mobile-facing antennas 1502-1504 to thesame diplexer 1506. It will be understood that the same arrangementillustrated in FIGS. 84 and 85 can also be used to provide wide-angleelevation coverage by simply rotating the structure 90° so that FIG. 84becomes a side elevation rather than a top plan view.

FIG. 86 illustrates an alternative technique for achieving wide-angleazimuth coverage by using a dipole 1510 as the mobile-facing antenna,with the adjacent surface 1511 of the flat-panel repeater 1512 servingas a flat reflector. The combination of the dipole 1510 and thereflector 1511 produces a wide-angle azimuth beamwidth. FIG. 87illustrates a modified repeater 1513 which forms a shaped (concave)reflector 1514 on the mobile-facing side to further increase the azimuthbeamwidth.

The antennas on opposite sides of the flat-panel repeater may also bemounted in planes that are not parallel to each other to reach thedesired coverage areas. For example, FIG. 88 illustrates a repeater 1520having a mobile-facing antenna 1521 lying in a plane that intersects theplane of the base-station-facing antenna 1522 at an angle θ to service amobile coverage area located in the direction of the beam axis 1523 ofthe antenna 1521.

The repeater may also be designed to re-transmit signals in a directionorthogonal to the direction in which the signals are received by therepeater. The orthogonal relationship of the two paths may be inazimuth, in elevation, or a combination of the two. For example, FIG. 89illustrates a repeater 1530 designed to receive horizontally propagatingsignals and re-transmit them vertically downward. Such a repeater isuseful, for example, when the repeater must be located above theintended coverage area, or where the signal-to-noise ration is best at alocation higher than the intended coverage area. In the illustrativeembodiment of FIG. 89, base station signals propagated along ahorizontal path are received by a vertically polarized monopole (ordipole) 1531 extending upwardly from one side (top) of the flat-panelrepeater 1530, and then re-transmitted vertically downward by a flat,horizontally polarized antenna 1532 on the opposite side (bottom) of therepeater. A ground plane 1533 for the antenna 1532 is provided on thelower surface of the repeater body which contains the electronics. Thepolarization difference between the two antennas 1531 and 1532 improvesthe isolation between the two antennas.

Referring next to FIG. 90, there is shown an antenna system forre-transmitting a GPS signal 1409 inside a structure 5. The antennasystem includes a link antenna 1412 for receiving the GPS signal 1409from a GPS transmitting antenna 1411, a GPS repeater 1414 for amplifyingthe received GPS signal 1410 to produce a second GPS signal 1415 and abroadcast antenna 1416 for re-transmitting the second GPS signal 1415inside the structure 5. This embodiment works best where the structure 5has the dimensions of a two-story building.

The GPS repeater 1414 feeds the received GPS signal 1410 into thestructure 5. In one embodiment, the external link antenna 1412 capturesthe GPS signal 1409 and feeds it to the GPS repeater 1414. The GPSrepeater 1414 boosts the received GPS signal 1410 and drives an internalbroadcast antenna 1416 that radiates the second GPS signal 1415 insidethe structure 5.

The present invention overcomes the inability of GPS receivers to workinside a structure, which is a major shortcoming of the GlobalPositioning System. As the GPS is used in more commercial applications,the ability to overcome this shortcoming becomes very important.Examples of commercial uses of the GPS include: Enhanced 911 service;wireless phone services that provide an Internet connection; wirelessservices that provide the location of, e.g., hotels, restaurants, andbusinesses; services that provide assistance to the elderly andhandicapped; and locator services (provide by, e.g., rental carcompanies) that provide location information that can be received insidestructures such as parking garages, buildings and tunnels.

In one embodiment, the GPS repeater 1414 includes the components shownin FIG. 92. Those components include a band pass filter 1418, a lownoise amplifier 1420, a gain block 1422, a power amp 1424 and secondband pass filter 1426. The band pass filters 1418 and 1426 are selectedso as to reduce the out-of-band signals. For a GPS repeater system, thepass band will usually be around 1575.42 MHz (+/−500 kHz). In oneembodiment, the gain block 1422 includes a radio frequency (RF)amplifier 1428, a band pass filter 1430 and a second RF amplifier 1432,as shown in FIG. 93.

In another embodiment shown in FIG. 94, the gain block 1422 includes amixer 1434 for down converting the GPS signal 1410 to an intermediatefrequency (IF) signal 1436. The GPS signal 1410 is combined by a mixer1434 with a local oscillator (LO) signal 1440 to produce the IF signal1436. In one embodiment, the IF is between about 140 MHz to 160 MHz,depending on the application. Thus, where the LO signal 1440 is 1640 MHzand the GPS signal 1410 is 1.5 GHz, then the IF signal would be 140 MHz.The IF signal 1436 is amplified by amplifiers 1442 and filtered by aband pass filter 1444. The band pass filter 1444 significantly reducesthe complex components or images of the GPS signal 1410 and the LOsignal 1440. A second mixer 1446 converts the IF signal 1436 to producethe RF signal 1438. The IF signal 1436 is combined by the second mixer1446 with the LO signal 1440 to produce the RF signal 1438. In oneembodiment, the IF is between about 140 MHz to 160 MHz, depending on theapplication. Thus, where the LO signal 1440 is 1640 MHz and the IFsignal is 140 MHz, then the RF signal 1438 is 1.5 GHz. Therefore, inthis embodiment, the RF signal 1438 is the second GPS signal 1415.

In one embodiment, the RF signal 1438 is an unlicensed frequency signal.The unlicensed frequency signal can be in any frequency range notlicensed by the Federal Communications Commission (FCC). Some examplesof unlicensed frequency bands include: 902-928 MHz and 2.4 GHz.

Referring to FIG. 91, there is shown an antenna system 1540 forre-transmitting a received GPS signal 1541 inside a structure 1542. Theantenna system 1540 includes a link antenna 1543 for receiving the GPSsignal 1541, a primary GPS repeater 1545 for amplifying the GPS signal1541 to produce an RF signal 1538, a first broadcast antenna 1547 tobroadcast the RF signal 1538 to one or more secondary repeaters 1650located to cover the intended coverage area inside the structure 1542.The RF signal 1538 is broadcast to the secondary repeater(s) 1650 ateither the original GPS frequency or another available frequency. In oneembodiment, the RF signal 1538 is in one of the unlicensed frequencybands such as the Instrumentation, Scientific and Medical (ISM)frequency band of 902 MHz-928 MHz. Each secondary repeater 1650 receivesthe RE signal 1538 via a link antenna 1544, amplifies the RF signal 1538to produce a second GPS signal 1546 and re-transmits the second GPSsignal 1546 via a second broadcast antenna 1548 inside the structure1542. The secondary repeater(s) 1650 may be placed inside the structure1542 or even placed external to the structure 1542 such that the RFsignal 1538 can be re-transmitted into the structure through the windowsor walls of the structure. This embodiment works best where thestructure 1542 has the dimensions of a multi-story building.

In one embodiment, the primary repeater 1545 includes the componentsshown in FIG. 95. Those components include a band pass filter 1549, alow noise amplifier 1550, a gain block 1551, a power amp 1552 and secondband pass filter 1553. In one embodiment, the gain block 1551 includes,as shown in FIG. 96, a mixer 1555 for down converting the GPS signal1541 to an IF signal 1557. The GPS signal 1541 is combined by a mixer1555 with a local oscillator (LO) signal 1554 to produce the IF signal1557. In one embodiment, the IF is between about 140 MHz to 160 MHz,depending on the application. Thus, where the LO signal 1540 is 1640 MHzand the GPS signal 1541 is 1.5 GHz, then the IF signal would be 140 MHz.The IF signal 1557 is amplified by amplifiers 1556 and filtered by aband pass filter 1562. The band pass filter 1562 significantly reducesthe complex components or images of the GPS signal 1541 and the LOsignal 1554. A second mixer 1558 up converts the IF signal 1554 toproduce the RF signal 1538. The IF signal 1554 is combined by the secondmixer 1558 with a second LO signal 1564 to produce the RF signal 1538.In one embodiment, the IF is between about 140 MHz to 160 MHz, dependingon the application. Thus, where the second LO signal 164 is 762 MHz andthe IF signal is 140 MHz, then the RF signal 1538 is 902 MHz.

In one embodiment, the secondary repeater 1650 includes the componentsshown in FIG. 97. Those components include a band pass filter 1618, alow noise amplifier 1620, a gain block 1622, a power amp 1624 and secondband pass filter 1626. In one embodiment, the gain block 1622 includes,as shown in FIG. 98, a mixer 1670 for down converting the RF signal 1538to an IF signal 1672. The RF signal 1538 is combined by a mixer 1670with a local oscillator (LO) signal 1678 to produce the IF signal 1672.In one embodiment, the IF is between about 140 MHz to 160 MHz, dependingon the application. Thus, where the LO signal 1540 is 742 MHz and the RFsignal 1538 is 902 MHz, then the IF signal would be 160 MHz. The IFsignal 1672 is amplified by amplifiers 1674 and filtered by a band passfilter 1676. The band pass filter 1676 significantly reduces the complexcomponents or images of the RF signal 1538 and the first LO signal 1678.A second mixer 1680 converts the IF signal 1672 to produce the secondGPS signal 1615. The IF signal 1672 is combined by the second mixer1.680 with a second LO signal 1682 to produce the second GPS signal1615. In one embodiment, the IF is between about 140 MHz to 160 MHz,depending on the application. Thus, where the second LO signal 1682 is1340 MHz and the IF signal is 160 MHz, then the second GPS signal 1615is 1.5 GHz.

Thus, the GPS repeater system of the present invention fills the GPSnull or “blank” areas within structures. In this way, the GPS can beused to locate individuals inside buildings, tunnels, garages, etc.

In another embodiment, the repeater system of the present invention isused in satellite transmission applications such as digital radio. LikeGPS applications, digital radio signals transmitted by satellites can beobstructed from receiving antennas by structures such as buildings, cargarages, tunnels, etc. Therefore, the claimed repeater is capable ofre-transmitting a satellite signal inside a structure such that anuninterrupted satellite signal can be transmitted to a receiver.

1. A modular repeater comprising: a housing having generally oppositely facing surfaces; at least one antenna positioned on each of said surfaces for radiating energy in generally opposite directions; electronic circuitry positioned in the housing and operatively coupling signals between the antennas, the electronic circuitry including feedback suppression structures for improving side-to-side isolation, wherein said antennas each comprise radiating antenna elements located centrally on an associated ground plane of sufficient area within the housing to contribute significant feedback suppression.
 2. The repeater of claim 1 wherein said electronic circuitry includes a digital adaptive cancellation system.
 3. The repeater of claim 1 wherein said electronic circuitry includes an automatic gain control circuit.
 4. A repeater comprising: a housing having generally opposing sides; a first antenna mounted closely adjacent to one of the generally opposing sides of said housing; a second antenna mounted closely adjacent to the other of said generally opposing sides of said housing; repeater electronics mounted in said housing and operatively interconnecting said antennas; and said repeater electronics including an interference cancellation circuit for effectively reducing interference feedback signals between said antennas in both an uplink path and a downlink path. 